U.S. Coast Guard and state investigative teams were working Friday at the Ohio River area where two off-duty FBI employees were killed in a collision between a barge and a small pleasure boat, trying to piece together how the accident occurred.

The two men's boat hit a 600-foot barge late Thursday in the river between Cincinnati and Newport, Kentucky. The two were found dead on the boat when fire crews arrived, authorities said.

"It is with great sadness that we advise that two FBI employees were involved in a tragic accident late last night," the FBI said in a statement Friday.

FBI spokesman Todd Lindgren said they were Cincinnati division employees but not special agents. They were identified as John Stack II, 29, and Bruce Eastlick, 28. No other information about them was released immediately.

Authorities said the barge was heading upriver, toward West Virginia. The boat's direction was under investigation. The first calls on the collision were made just before 11 p.m. Thursday, authorities said. Local fire departments from both sides of the river responded initially.

Among possible factors under investigation by the Coast Guard and the Kentucky Department of Fish and Wildlife Resources were whether speed or alcohol was involved, and whether the pleasure boat was lit up.

"The Coast Guard will conduct a thorough investigation," Capt. Richard Timme, Coast Guard commander for Ohio Valley, said in a statement.

Chief Warrant Officer Jonathan Roy said he couldn't estimate a timetable for the completion of the investigation.

Cincinnati District Fire Chief Lou Arnold told The Cincinnati Enquirer that the barge captain was at the wheel and saw the collision.

"He was looking right out the front watching what was going on. It was a big barge," Arnold said. "The (pleasure boat) just crossed right in front of them and slammed into the barge. We can only assume they didn't see it."

Kenneth Kidwell said he was near the accident scene Thursday night.

"It was very loud ... very loud," Kidwell told WCPO-TV. "Metal on metal."

Emergency crews searched the river through the night to make sure there was no one who had been thrown overboard.